Abstract
Glasses with compositions corresponding to stillwellite-type (La,Ln)BGeO5 (Ln: Nd, Gd, Eu and Tm) crystalline phases have been prepared, and the effect of lanthanide substitutions on ferroelectric properties and second harmonic (SH) intensities of stillwellite-type crystalline phases formed by crystallization of glasses has been examined. The substitution of Ln3+ for La3+ ions in the LaBGeO5 phase has been confirmed from the results of X-ray diffraction (XRD) analysis and fluorescence spectra of Eu3+ ions. The substitution of Ln3+ for La3+ ions causes a decrease not only in the lattice constants but also in the a/c axis ratio. The amount of substitutions depends on the Ln3+ ionic radius. The Curie temperature of crystallized glasses increases almost linearly with decreasing mean ionic radius of lanthanides estimated from the composition of base glasses. A similar trend is observed in the SH intensity for crystallized glasses (powdered form), indicating the presence of a close relationship between Curie temperature and SH intensity. It is proposed from Raman spectra that the enhancement of SH intensities is caused by the change in the arrangements of BO4 and GeO4 tetrahedra in the (La,Ln)BGeO5 crystals due to the substitution of Ln3+ ions having stronger Ln3+–O bonds. A clear second harmonic generation is observed in transparent surface crystallized glasses of the Nd2O3- or Gd2O3-substituted system.
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